Petrogenesis of a aluminous A-type granite from Munnar, southwestern India

A suite of alkali granite and syenite plutons preserving evidence for a prominent Pan-African felsic magmatic event intrudes the Proterozoic granulite facies terrains of southwestern part of the Indian Peninsula. The alkali granite near Munnar, southern Kerala, forms part of this suite. Its spatial association with regional lineaments implies that the orientation of the intrusive is directly controlled by the local fault system, and indirectly controlled by the rate of magma intrusion and heat loss into the surrounding metamorphic rocks. The field relations and undeformed igneous textures indicate the post-deformation nature of the magmatism. Geochemical features characterize the Munnar granite as aluminous A-type granite. Within the constraints imposed by the high temperature, anhydrous, K-rich nature of the magma, trace element modelling, and comparison with recent experimental studies on various granitoid source compositions, the distinctive features of the Munnar granite are suggested to reflect a source rock of igneous charnockitic (C-type) nature. We propose a petrogenetic model involving fractional crystallization of a charnockitic lower crustal magma for the Munnar granite, the source composition represented by the intermediate massif charnockites from the near by Kodaikanal-Cardamom hill.